Civil servants' medical records have been stolen in the latest government data loss.

Sensitive files on staff - which included letters written by doctors - were smuggled out of a supposedly secure office by a thief who broke into a locker. An insider at the Department for Work and Pensions revealed: "Bosses have no idea how it happened. It's a farce.

"These are bulky files that vanished despite CCTV and security guards." The 28 files went missing from the document management team office at the Hilden House DWP Pension Centre in Warrington, Cheshire, around August 4.

But a source said it was two weeks before the loss was noticed. The files are thought to concern 14 staff. The DWP said: "The incident will be investigated." It is the latest in a line of government data losses.

Bank details of 25 million people were lost by HM Revenue and Customs and DWP papers on benefit claims were found dumped.